linux-kernel - [PATCH v2 0/1] tick/nohz: avoid showing '(null)' if nohz

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Message-ID: <20251007012504.16118-1-atomlin@atomlin.com>
Date: Mon,  6 Oct 2025 21:25:03 -0400
From: Aaron Tomlin <atomlin@...mlin.com>
To: gregkh@...uxfoundation.org,
	rafael@...nel.org,
	dakr@...nel.org
Cc: riel@...riel.com,
	frederic@...nel.org,
	atomlin@...mlin.com,
	linux-kernel@...r.kernel.org
Subject: [PATCH v2 0/1] tick/nohz: avoid showing '(null)' if nohz_full= not set

In the context of CONFIG_NO_HZ_FULL=y, tick_nohz_full_mask (of type
cpumask_var_t) is initialised to 0. Memory is only allocated to the cpumask
data structure, when Linux kernel boot-time parameter "nohz_full=" is
correctly specified (see tick_nohz_full_setup() and housekeeping_setup()).
If "nohz_full=" is not set and an attempt is made to read
/sys/devices/system/cpu/nohz_full, '(null)' can be displayed:

    ❯ cat /sys/devices/system/cpu/nohz_full
    (null)

This patch changes the output to print a newline (or 0x0A) instead of
'(null)', making it consistent with print_cpus_isolated() behaviour.

Changes since v1 [1]:

 - Refactor to use an if statement (Greg KH)

[1]: https://lore.kernel.org/lkml/20251006005824.76187-1-atomlin@atomlin.com/

Aaron Tomlin (1):
  tick/nohz: avoid showing '(null)' if nohz_full= not set

 drivers/base/cpu.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

-- 
2.49.0